1. Technical Field
The present invention relates to a display device and a control method for the display device.
2. Related Art
There has been known a display device mounted on the head of a user (see, for example, JP-A-2006-12042 (Patent Literature 1)). In a display device that emits light, in general, the intensity of the light emitted by the display device, in other words, the luminance or the brightness of display can be adjusted. The same applies to the display device mounted on the head.
There has been known a display device that secures the visibility of a displayed image and a displayed video when the display image and the displayed video are affected by light in the outside world (also referred to as external light) (see, for example, JP-A-2006-139124 (Patent Literature 2)). A head mounted display (HMD) disclosed in Patent Literature 2 irradiates light to the outside world in order to display a video and secure a preferred visual field even in a dark place. The display device differentiates a color directly recognized by a user from the external light and a color recognized from video light irradiated by the display device to make it easy to distinguish the displayed video from the outside world.
When the eyes of a user and a display device are close to each other as in the display device described in Patent Literature 1, it is requested to set the luminance of display according to preference of the user. The feeling of brightness of display of the display device is affected by not only the sense of the user but also other factors such as the external light made incident on the eyes of the user. For example, it is likely that the feeling of the luminance of the display of the display device is substantially different when the light emitted from the display device and the external light are made incident on the eyes of the user from the same direction and when the external light is not made incident on the eyes. Therefore, control concerning the luminance of the display of the display device tends to be complicated, a processing load increases, and it is difficult to adjust the luminance as desired by the user.
When the device outputs the light to display a video and an image as described in Patent Literature 2, the appearance of the light output by the device changes according to the influence of other light. Patent Literature 1 discloses an example in which the wavelength of image light is set to a wavelength different from the wavelength of light irradiated to the outside world by the device. However, in this example, the wavelength of the irradiated light is known. On the other hand, when the wavelength of light affecting the visibility of an image displayed by the display device cannot be specified in advance, measures cannot be taken.